euler47

astro1138/euler47.hs

@@ -0,0 +1,24 @@
+import Data.List (nub, intersect)
+import Debug.Trace (trace)
+
+primes :: Int -> Int -> [Int]
+primes n d | d <= n = if n `rem` d == 0
+                      then d:(primes (n `div` d) d)
+                      else primes n (d + 1)
+primes _ _ = []
+
+--primefactors n = trace ("primefactors " ++ (show n)) $ primes n 2
+primefactors n = primes n 2
+
+has_dups [l] = False
+has_dups (a:b:l) | a `intersect` b /= [] = True
+                 | otherwise = has_dups (b:l)
+
+euler47' a numbers | is_desired = numbers'
+                   | otherwise = euler47' a rest'
+    where numbers' = take a numbers
+          factors = map (nub . primefactors) numbers'
+          is_desired = all (((==) a) . length) factors && (not $ has_dups factors)
+          (_:rest') = numbers
+
+euler47 = euler47' 4 [2..]